Information on the May 22, 2011 Tornado Event

 Information on this webpage is considered preliminary and will continue to be updated as the event is analyzed.

Anyone with information that could enhance the record of these storms should contact the National Weather Service Office in Tulsa at 918-838-7838 during business hours, submit an online storm report, or send us an email at: Information can also be posted on our Facebook page.


Event Summary - May 22, 2011 Severe Thunderstorm and Tornado Event and May 23, 2011 Flooding

Survey teams from the NWS office in Tulsa are investigating damage from tornadoes that occurred on May 22, 2011.  The surveys initially focused on several areas of reported damage in Delaware County, Oklahoma, and Benton County, Arkansas.  Additional areas will likely be investigated over the next several days. 

Information about the Joplin tornado can be found from the NWS Springfield office.

A dryline extended from southeast Kansas into southwest Oklahoma on the afternoon of May 22, 2011.  An extremely unstable airmass, with CAPE values near 5000 j/kg, was in place ahead of the dryline across eastern Oklahoma and northwest Arkansas.  Several thunderstorms developed along the boundary across northeast Oklahoma by early evening, with more isolated convection occurring further south in southeast OK.  These storms quickly became severe, and rotating supercells produced large hail, wind damage, flash flooding, and tornadoes as they tracked east across eastern Oklahoma and northwest Arkansas.  Later in the evening, additional severe thunderstorms developed along outflow boundaries that had been produced by the early storms.  See the map below for some preliminary local storm reports from this event.

An outflow boundary from May 22 lingered across northeast OK and northwest AR on May 23.  Training of thunderstorms along and north of this boundary led to very heavy rainfall and extreme flash flooding.  These storms eventually developed in a MCS. This complex moved through east central OK and west central AR and produced wind damage along its path.  The mesonet site in Vinita measured 7.48” of rain in only 5 hours!  For context, according to the USGS Depth-Duration Frequency of Precipitation for Oklahoma map, the 0.2% annual chance 6-hour rainfall for Vinita is approximately 7”.  Rainfall totals for Nowata, Craig, and Ottawa Counties were 3” to 10”.  Roads, as well as creeks and streams, remained flooded in these areas for several days.  Very heavy rain also occurred in northwest AR.  3.07” of rain was measured in 1 hour at the Fayetteville/Drake Field airport (KFYV) between 3 and 4pm on May 23.  The NWS Prairie Grove COOP observer measured 6.62” during the 24-hour period from 7am 5/23-7am 5/24.  Widespread 3” to 5” affected Benton and Washington Counties in AR, with much of the remainder of the area receiving 0.5” to 3” of rain.  All of this rainfall also led to mainstem river flooding.  The Illinois River near Watts reached major flooding, cresting at 25.19' at 7am CDT on May 24.  As this flood wave moved downstream, major flooding also occurred along the Illinois River near Tahlequah, with a crest of 21.12' at 4am CDT on May 25.


Information from this event is still considered preliminary and will be modified based on additional information that may become available to us.  Anyone with information that could enhance the record of this event should contact the National Weather Service Office in Tulsa at 918-838-7838 during business hours, or send us an email at, or submit an online report.

Preliminary Tornado Information (last updated 11:00 pm 5/24/11):

Images of the tornado damage can be found by clicking on the tornado triangle symbols in the map below. 

Grove Tornado (Delaware County-McDonald County MO)

Began: 2.5 miles west-southwest of Zena at 6:52 pm                   Ended: 8.7 miles east-southeast of Grove at 7:25 pm (continued into Missouri)

Path Length: 16.5 miles          Max Path Width: 1550 yards

EF Rating:  EF-3 (max wind speed 140 mph).  Two double-wide manufactured homes were destroyed, a permanent home was severely damaged, barns and outbuildings were destroyed, a number of other homes were damaged, many hundreds of trees were snapped or uprooted, and many power poles were snapped.


Grand Lake Tornado (Delaware County)

Began: 1.8 miles south of Cleora at 6:33 pm        Ended: 5.1 miles west-southwest of Grove at 6:48 pm (further surveys may yield slightly different beginning/ending points)

Path Length: 6.7 miles          Max Path Width: 800 yards

EF Rating:  EF-2 (max wind speed 130 mph).  Several homes were severely damaged, seven mobile homes were destroyed, boat docks were destroyed, many other homes were damaged, many trees were snapped or uprooted, and many poles were snapped.


Leach Tornado (Delaware County)

Began: 2.1 miles northwest of Leach at 8:13 pm                   Ended: 1.9 miles north of Twin Oaks at 8:23 pm

Path Length: 4.7 miles          Max Path Width: 400 yards

EF Rating:  EF-1 (max wind speed 105 mph).  Trees snapped and uprooted.  Several homes damaged.  Barns damaged or destroyed.


Kansas Tornado (Adair/Delaware County)

Began: 2.5 miles north of Chewey at 8:14 pm                   Ended: 5.2 miles east of Kansas at 8:19 pm

Path Length: 4.5 miles          Max Path Width: 200 yards

EF Rating:  EF-2 (max wind speed 115 mph).  Several small homes destroyed.  Barns and outbuildings destroyed.  Trees snapped or uprooted. 


West Siloam Springs Tornado (Delaware County)

Began: 5.3 miles west of West Siloam Springs at 8:30 pm                   Ended: 3.6 miles northwest of West Siloam Springs at 8:37 pm

Path Length: 2.9 miles          Max Path Width: 350 yards

EF Rating:  EF-2 (max wind speed 125 mph). Tornado destroyed six mobile homes, injuring 12 people.  Trees were snapped or uprooted. 


Gentry Tornado (Benton County)

Began: 3.2 miles southwest of Gentry at 8:54 pm                   Ended: 1.3 miles northwest of Gentry at 9:00 pm

Path Length: 2.8 miles          Max Path Width: 450 yards

EF Rating:  EF-1 (max wind speed 105 mph).  Trees snapped or uprooted.  Several barns damaged. 


 Image captions below the image.  Click on image to open a larger version in a new window. Please only use images with permission from the owners listed. Additional images can be found in the Event Map below.

funnel near Zena, OK
large hail at NWS Tulsa office large hail at NWS Tulsa office
Photo of a funnel cloud and possible tornado near the community of Zena in Delaware County shortly before 7 pm. Photo by Ashley Hampton
Tennis ball to baseball sized hailstone that fell at the NWS Tulsa office at 1046 pm. Photo by NWS Tulsa
Golf ball to baseball sized hail that fell at the NWS Tulsa office at 1046 pm. Photo by NWS Tulsa
Tornado near Oaks 24 hour rainfall total  
Tornado north of Oaks (Delaware Co.) Picture taken 2NE Oaks looking north northwest. Photo by Jeff Smith  24-hour rainfall total ending at 7am May 24, 2011  


Preliminary Event Impact Map This map will be updated as additional information is received.  Click on the icons within the map for additional details and/or images related to that impact.  Tornado information can be found by clicking on the track.

Tornado Tracks: Due to mapping/GPS software differences and road accessibility along the track, use the plotted tracks for general reference only. Tornado tracks may be updated and/or changed due to storm damage surveys, data analysis, and eyewitness reports.

Storm Survey: Colored icons represent the Storm Survey rating assigned to surveyed damage. Click on the icon for additional information and available photos. You may need to zoom in tightly to see all the available data points when data points are logged close to one another.  Links to photos are available in the upper portion of the text window that opens when you click on one of the colored data icons or points.

Hail, Wind, and Flood Reports: Click on the icon for the time, location, and description of the storm report. Click here to submit your storm report.

Other Data: Additional data or images from the event.

Survey Legend


Maps+: Counties:


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